Exactly, it is cumulative, and then it gives a specific example of how it combines with the grade reduction, which includes the rounding.
This rebate is cumulative with the reduction offered by the chosen 'ware's grade, if any (e.g., the reduction for alphaware of 0.8 is reduced by ten percent, or 0.08, to become 0.72, and is rounded down to 0.7).
Based on that, it is clear that the intent was for the reduction by ten percent to be applied to the essence cost multipliers of the various grades.
GRADE | ESS COST MULT. | ESS COST MULT W/ BIOCOMPAT. |
Standard | x 1.0 | x 0.9 |
Alphaware | x 0.8 | x 0.7 |
Betaware | x 0.7 | x 0.6 |
Deltaware | x 0.5 | x 0.4 |
Used | x 1.25 | x 1.1 |
Each of those calculations is "reduced by ten percent, rounded down to the nearest tenth" it results in 'ware costs that make sense and you don't have any weird non-essence ware.
Yes, they could have phrased it differently to make it clearer, but as you pointed out in your OP, it seems odd to have 'ware essence cost get rounded down to 0 (because it shouldn't).
In the good old days, we would have just not had any phrasing about rounding and you have street sams calculating their essence out to ten-thousandths of a point.